INTRODUCTION This report has been developed as a guide for use by the refinery operator for evaluating the potential impact of his impoundments on the ground-water resources underlying the refinery. In addition@ this guide may be used to assist the data-collection program necessary to evaluate the ability of refineries to meet various requirements imposed by environmental regulation on the construction and operation of refinery impoundments. Due to the currently indeterminate form of the regulations concerning solid and hazardous waste handling which will be implemented by EPA and the states under the Resource Conservation and Recovery Act (RCRA)@ this guide does not address a specific set of regulatory criteria but rather attempts to provide a means for evaluating refinery impoundments with respect to a broader spectrum of potential regulatory criteria. The criteria included in this guide are drawn from the proposed RCRA regulations of December 1978@ and from potential regulatory approaches and criteria developed both in existing state regulatory programs and by scientists working in the areas of waste management. This guide contains only the basic hydrogeologic and siting criteria and does not address monitoring@ diking@ runoff control@ or liner criteria which may be included in some regulatory programs. A brief discussion on monitoring philosophy is included@ however.